Following a precatory proposal from billionaire investor and Apple shareholder Carl Icahn urging Apple to vote on a larger buyback, Icahn today announced on Twitter that he thinks Apple “is doing great disservice to shareholders by not having markedly increased its buyback.” He also said that he would soon send Apple another in-depth letter regarding his proposals and confirmed that he has purchased another $500 million in Apple shares bringing his total investment to $3 billion. 

After months of letters and meetings with Tim Cook urging the Apple CEO to introduce a larger buyback at around $150 billion, last month Icahn said he gave Apple notice that he would be making a precatory proposal to shareholders to call for a vote on a buyback at less than the $150 billion he originally proposed. A precatory proposal is essentially a formal request asking Apple to hold the vote, but it means Apple executives wouldn’t actually have to implement the buyback even if the majority of shareholders approved it.

Icahn has been proposing a larger buyback from Apple of around $150 billion since first announcing back in August that he had taken “a large position” in the company. We now know that position has increased from the $2.5 billion he owned previously to around $3 billion.

Icahn previously said executing the buyback immediately would result in “further stock appreciation of 140% for the shareholders who choose not to sell into the proposed tender offer.” He also agreed to withhold his shares and not participate in the buyback to “invalidate any possible criticism” regarding the long term benefits of the proposal.

Apple confirmed that it received the precatory proposal and said it would actively seek shareholders’ input and announce any changes to its return program in the “first part of calendar 2014.”